1. Field of the Invention
The present invention relates to a terminal controller and, more particularly, to improvements in a terminal controller which operates to buffer screen data coming from a central processing unit and for transferring this data to a terminal device.
2. Description of the Prior Art
Conventionally, when sending screen data to a terminal device, such as a display or printing device, it is usual to edit the data sent from a central processing unit by means of a terminal controller, and to transfer the edited data to a buffer memory belonging to the terminal device. The terminal controller is equipped with a screen data editing buffer memory which corresponds to the buffer memory in the terminal device and on which the screen data is edited, until the edited screen data is sent to the terminal device.
In the operations of the terminal controller thus far described, the process of editing the screen data takes the longer time because the screen data is more complex. This delays the response time from the viewpoint of the terminal device. This terminal device performs the operations of adding keyed-in data to the initial screen given from the terminal controller, and operates to send either the data of the whole screen or only the additional data to the central processing unit through the terminal controller. The above processes for an identical initial screen could sometimes be repeated, so that the terminal controller repeats the identical editing process for the identical screen data, and this raises a performance problem especially in the case of a complex initial screen. Since the central processing unit repeatedly sends the identical screen data to the terminal controller, moreover, the circuit usage is wasteful, especially when communication lines, etc., are used, thus inviting a disadvantage in the cost for the use of the communication line and so on.